The disclosure relates generally to the milling of components, and more specifically includes portable milling tools and methods of milling a rotor-mounted turbomachine component.
Large industrial machines, such as turbomachines, can include a wide variety of large, expensive parts that are stressed during operation. In order to reduce the costs of operating the industrial machines, it is advantageous to extend the lifespan of these parts for as long as safely possible. In order to extend the lifespan of parts, stress relief techniques may applied to create a less stress-inducing structure, e.g., a cut recess with less-sharp corners that may exhibit increased stress. Stress relief techniques may also be advantageous to apply to extend the lifespan of parts already in use in the field.
Turbines include a number of large blades that are coupled to a rotor using slots in the rotor, i.e., mating dovetail connections. During operation, the blades rotate with the rotor as a fluid is forced across the blades, or the blades are forcibly turned to move the fluid. During operation, the blade and rotor connections can be stressed. For example, an end face of the rotor slot, oftentimes a dovetail shape, may include a cooling channel flange that creates a cooling channel at the end face of the slot. A corner at which the flange integrally couples to the end face of the slot may observe high stresses. In order to provide safe operation due to the various stresses, a rotor wheel may be scrapped after, for example, 100,000 hours. Since replacement of a rotor wheel is extremely costly, whatever stress reducing techniques are possible to extend the lifespan of the disk are ideally implemented during manufacturing. However, in some instances, it is possible to apply stress-relieving revisions to a rotor in the field to provide additional stress reduction.
Providing stress reducing techniques to rotors in the field, however, presents a number of challenges. The geometrical profile of a dovetail slot can vary widely from turbomachine to turbomachine, and from wheel to wheel within a single turbomachine. Some dovetail slots may include, for example, two or more sidewalls which meet at an acute angle to form a sharp sidewall region. In some cases, the material composition of a wheel may experience wear following extended use of the turbomachine. The dovetail slots of a wheel may be difficult to access or repair with conventional tools or repair techniques. Some specially-equipped machining shops may be capable of performing sophisticated repairs in these areas of the component. However, this approach may be costly in situations where a turbomachine is remote from the location of a machining shop.